Twin-wire paper forming with wires wrapping around a suction web-forming breast roll and then following a curved path to a suction couch roll

ABSTRACT

1. Improvement in a two-wire former in a paper machine, comprising in combination, a web-carrying wire and a covering wire; two rolls with foraminous mantle surfaces within the loop of said carrying wire, wherein the one which is first in the direction of travel of the web is a web-forming roll and the second is a couch roll; dewatering compartments within the mantle of said rolls, at least one in each; said carrying wire and covering wire running along a common curved path starting at said web-forming roll and up to said couch roll, this path forming a convex part of the loop of said carrying wire, the course of said curved path being determined by the positions of at least one wire-guiding means and furthermore at least one dewatering means placed within the loop of said web-forming roll each over its individual first and second wire-guiding roll to thereafter form a throat therebetween, means for adjusting the position of each of said first and second wire-guiding rolls; furthermore a headbox, which supplies pulp into said throat; the whole combination being such that the bulk of the dewatering of the web takes place at said web-forming roll on the sector, having a size of 90 to 150 degrees of arc, lapped by said wires, primarily by effect of the pressure developed in the pulp suspension between said wires the expressed water being removed on effect of the centrifugal force outwards and partly in the opposite direction into said web-forming roll.

M. KANKA ANPAA 3,846,232 -WIHE PAPER FORIING WITH WIRES WRAPPING AROUND A win: I

sucuon WEB-FORIIING sans: ROLL AND rum: FOLLOWING A cunvsnnm'm 1'0 rsucnox couca ROLL 2 Shuts-Shut 1 Filed larch 23, 1973 PZMEPmQAE M. KANKAANPAA Nov. 5, 1974 TWIN'WIRE PAPER FORMING WITH WIRES WRAPPING AROUND A SUCTION WEB-FORMING BREAST ROLL AND THEN FOLLOWING A CURVED,,PATH TO A SUCTION COUCH ROLL 2 Shuts-Shut 2 Filed March 23, 1973 United States Patent Otfice 3,846,232 Patented Nov. 5, 1974 US. Cl. 162--301 3 Claims ABSTRACT OF THE DISCLOSURE A two-wire papermaking system which includes a looped web-carrying wire and a looped covering wire which together form a throat adjacent a suction web-forming breast roll and thereafter wrap around the breast roll along 90 to 120 degree are. A headbox discharges slurry into the throat between the two wires. Subsequent to the webforming roll the wires move along a curved path (formed by a wire-guide roll and a dewatering foil) and wrap around the surface of a suction couch roll located within I the loop of the web-carrying wire. Adjustably positioned wire guiding rolls located within the looped web-carrying and cover wires prior to the web-forming breast roll allow for adjusting the throat size. Centrifugal dewatering occurs as the wires wrap around the web-forming roll. Slurry is discharged into the throat at a rate less than the speed of the wires.

The present invention concerns, in a paper making machine, a two-wire former wherein drainage of the paper web in the process of being formed takes place simultaneously through the carrying wire and the covering wire, and within which carrying wire there are two rolls with foraminous mantles, the first of these in the direction of travel of the web being a web-forming roll and the second a couch roll, and said web-forming roll comprising at least one dewatering compartment inside the shell and under the drainage zone, which is the sector that is covered by both wires and Where drainage of the fibre suspension is primarily achieved by bringing the wires together and which zone has most appropriately a length of 90 to 120 degrees of arc, said carrying wire and covering wire forming, adjacent to the web-forming roll and prior to its drainage zone, a throat, into which the headbox supplies fibre suspension.

In recent years a number of so-called twin-wire former constructions have been developed, wherein drainage of the paper web that is being formed takes place in two directions simultaneously. It is obvious that the drainage is appreciably speeded up by this principle of operation. In addition, the resulting paper web has a more nearly homogeneous structure than that produced by the aid of a conventional Fourdrinier wire, where drainage takes place in one direction only.

In the original two-wire former aiming at symmetrical drainage, the path of the wires was vertical, and the slurry was fed from above into the gap between the wires, The newer types of two-wire formers differ from the original type, and mutually, mainly as regards the direction in which the pulp slurry is introduced between the wires and in the manner in which the joint travel of the wires has been arranged on that length of path where the web formation and the compaction of the web between these wires take place.

It has been found advantageous in most instances to boost the drainage by the aid of centrifugal force, by designing a such two-wire combination so that the wires have to travel through a curved path, especially in the initial section following immediately after the headbox, where the main part of the drainage takes place.

One design solution of this kind is represented by the construction disclosed in the British Pat. No. 993,837, wherein the wires pass around two rolls and thus describe a path resembling the letter S. The drawback of this structural type, and of its different variants, is that the wire that has lapped the first roll in the position of the inner wire will run as the outer wire over the second roll. This implies that the wires undergo a displacement with reference to each other and which may damage the fibre web, already formed, which is running along between them either by interfereing with its fibre orientation or by detracting from its strength.

'Ihose previously known designs wherein both the wires, throughout their common path, and the paper web hereby formed are curved in one direction only, include those of the Finnish Patent Applications No. 3,319/ 68 and 2,5 65. These have, for instance, the drawback that the curved path of the wire is accomplished by the aid of numerous and various means which rub against the wire (a curved-surface suction shoe or equivalent) and which have a powerful abrasive effect on the wire. The considerable space required by such constructions in the longitudinal direction of the paper machine can also be considered an objectionable feature.

The aim of the present invention is to accomplish an efiicient dewatering unit of minimum size, compared with its production output, and which therefore would be inexpensive to construct and would be conducive to economy as regards the room space in the paper machine hall. A further objective of the invention is to achieve highest possible symmetry of the dewatering of the fibre web, that is, equal removal of water through both surfaces of the web, yet in such manner that the above-mentioned drawbacks observed in connection with constructions of prior arts are avoided.

The invention is described in detail with reference to the figures of the attached drawing, wherein FIG. 1 shows, as a schematical elevational view, one embodiment of the invention while FIG. 2 presents another, slightly different embodiment example. Figure 1a shows the foil type sealing lists.

The construction shown in the figures comprises two foraminous dewatering rolls 4 and 5 disposed within one and the same carrying wire loop. A carrying wire is understood to be an endless wire upon which the paper web rests after the forming process and from which the web is picked up in a conventional manner for its further conduction into the press section of the paper machine. The one of these rolls which is first in the direction of travel of the web 3 is a web-forming roll 4. The carrying wire 1 lapping the web-forming roll 4 and the covering wire 2, conducted into conjunction with the first wire, form a throat 12, into which the fibre suspension is supplied from the headbox 11. In order to prevent flooding, that is filling of the throat 12, and to prevent transversal and undesired currents, the peripheral velocity of the web-forming roll 4 and correspondingly the speed of the wires should be higher than the velocity of the pulp slurry jet. The angle, or size, of the throat 12 can be regulated by changing the position of the first and second wire guiding rolls 8a and 7b. Thus also the pressure developed in the pulp slurry between the wires 1 and 2 can be regulated. The drainage begins efliciently, and symmetrically, in the throat 12 itself and continues thereafter on the web-forming roll 4 as a result of the pressure between the wires 1 and 2. The water expressed from the pulp slurry escapes outwardly under centrifugal force efiect and also into the web-forming roll 4, through the holes or openings in the roll mantle. Suction aids the emptying of the holes. In certain operating conditions this suction is achieved without vacuum pump by using foil type sealing lists 16 in the dewatering compartment inside the shell mantle of the Web-forming roll. If the dewatering caused by centrifugal force tends to produce a symmetry at high running speeds, the covering wire 2 may be chosen to have a sufiiciently fine mesh. To counteract the centrifugal force in certain conditions the dewatering compartment of the wveb-forming roll can be connected to a vacuum system ad the vacuum can be adjusted in accordance with the operation requirements.

After leaving the web-forming roll 4, the wires 1, 2 are carried together along a slightly curved path to the couch roll 5. The path is required to be curved in order to hold the wires 1 and 2 close together over the whole distance in question without need of applying any excessive tension or stretch to the covering wire 2. In order that the path jointly travelled by the wires might be curved, one may use a few guiding means 10, 14 between the dewatering rolls 4 and 5. The guiding means 10, 14 are either rotatable rolls or one or more fixed and narrow foils or deflectors 14, which exert the least possible abrasive effect on the wire 1. The approximate curvature of the joint path of wires is depicted in FIGS. 1 and 2 and defined by radius R The positive contiguity of the wires 1 and 2 may be assisted by means of a defiector 13 disposed on the side of the covering wire and which both urges against the wire and also serves as a dewatering means.

The couch roll 5, too, has most appropriately at least one dewatering compartment on its sector 7 connected to a suction system.

In order to dispose the water expressed from the paper web 3 on the run between the web-forming roll 4 and the couch roll 5, a small number of appropriate water removal means have been provided on either side of the wire run, such as deflectors 13, which have been disposed so as to present a minimum of edges rubbing against and causing abrasion of the wires 1, 2. It is also noted that these means exert no strong pressure against the wires 1, 2. The small number of water disposal means also enables the distance between the web-forming roll 4 and the couch roll 5 to be kept comparatively short, this distance being most appropriately 1.5 to 2 times, but at the most 3 times, the diameter 2R of the roll 4. The wire length that has been saved hereby can be utilized on the part of the path where the tension and guiding rolls 8 and 7, respectively, of the wires 1, 2 are found and whereby reliable arrangements can be made for the guidance of the wires. The loop of the carrying wire 2 has been shaped to constitute a part having an elongated extension in the horizontal plane and trasporting the web forward, from which part the web is picked off by the aid of a suction roll 9.

The water removed at the web-forming roll 4 is collected in save-alls a provided for this roll alone and it is conducted to the intake of the mixing pump supplying the head box 11, to be used as diluting water.

The water coming from the dewatering means 6, 14 and from the couch roll 5, which usually has a lower fibre content than the water obtained from the webforming roll, is collected in separate save-alls 15b, to be conducted to a point in the water system where a lower fibre content is desired.

It is also essential in the invetnion that the path jointly travelled by the wires 1, 2 curves in the same direction all the time (R R R The following inequalities of the radii R R R are also significant: 1 2; a i- As regards the guiding of the covering wire 2, this is arranged by means of the guiding roll 7b adjacent to the web-forming roll 4, and which guiding roll 7b is displaceable so that the angle of the throat 12 and the length of the throat 12 can be adjusted as required. At the couch. roll 5, the covering wire 2 laps the third wire guiding roll 7a, which in its one extreme position serves as a couch presser roll and presses the fibre web 3 against the suction zone 7 of the couch roll 5 for more efiicient dewatering. The position of the wire guiding roll 7a and thus the pressure of the wire against the couch roll 5 can be regulated, and in the other extreme position of the roll 7a (FIG. 2) the covering wire 2 can be made to cover the whole suction zone 7 of the couch roll 5.

I claim:

1. Improvement in a two-wire former in a paper machine, comprising in combination, a web-carrying Wire and a covering wire; two rolls with foraminous mantle surfaces within the loop of said carrying wire, wherein the one which is first in the direction of travel of the web is a web-forming roll and the second is a couch roll; dewatering compartments within the mantle of said rolls, at least one in each; said carrying wire and covering wire running along a common curved path starting at said web-forming roll and up to said couch roll, this path forming a convex part of'the loop of said carrying wire, the course of said curved path being determined by the positions of at least one wire-guiding means and furthermore at least one dewatering means placed within the loop of said carrying wire, and furthermore the carrying wire and covering wire both being conducted onto said web-forming roll each over its individual first and second wire-guiding roll to thereafter form a throat therebetween, means for adjusting the position of each of said first and second wire-guiding rolls; furthermore a headbox, which supplies pulp into said throat; the whole combination being such that the bulk of the dewatering of the Web takes place at said web-forming roll on the sector, having a size of to degrees of arc, lapped by said wires, primarily by effect of the pressure developed in the pulp suspension between said wires the expressed water being removed on effect of the centrifugal force outwards and partly in the opposite direaction into said web-forming roll.

2. Two-wire former according to claim 1, wherein said covering wire has a finer mesh than said carrying wire for achievement of a symmetrical dewatering action.

3. Two-wire former according to claim 1, further comrising at third wire guiding roll disposed within the loop of said covering wire and adjacent to the said couch roll, and means to adjust its position with reference to said couch roll.

References Cited UNITED STATES PATENTS 3,726,758 4/1973 Parker et al. 162-301 X 3,582,467 6/1971 Gustafson et al. l62303 2,274,641 3/1942 Abbott et al. 162-371 3,272,692 9/1966 Hayes et al. l62370 X OTHER REFERENCES Evans and Waelde: Significant Trends in Machine Design and Operation-I, in Paper Trade Journal, Aug. 9, 1971, pp. 30-35.

S. LEON BASHORE, Primary Examiner R. H. TUSHIN, Assistant Examiner US. Cl. X.R. 

1. Improvement in a two-wire former in a paper machine, comprising in combination, a web-carrying wire and a covering wire; two rolls with foraminous mantle surfaces within the loop of said carrying wire, wherein the one which is first in the direction of travel of the web is a web-forming roll and the second is a couch roll; dewatering compartments within the mantle of said rolls, at least one in each; said carrying wire and covering wire running along a common curved path starting at said web-forming roll and up to said couch roll, this path forming a convex part of the loop of said carrying wire, the course of said curved path being determined by the positions of at least one wire-guiding means and furthermore at least one dewatering means placed within the loop of said web-forming roll each over its individual first and second wire-guiding roll to thereafter form a throat therebetween, means for adjusting the position of each of said first and second wire-guiding rolls; furthermore a headbox, which supplies pulp into said throat; the whole combination being such that the bulk of the dewatering of the web takes place at said web-forming roll on the sector, having a size of 90 to 150 degrees of arc, lapped by said wires, primarily by effect of the pressure developed in the pulp suspension between said wires the expressed water being removed on effect of the centrifugal force outwards and partly in the opposite direction into said web-forming roll. 